Bio Mechanics Of The Shoulder

Biomechanics of the Shoulder

Osteology • The shoulder complex formed by Sternum Clavicle Scapula Humerus

Osteology Manubrium

Body

Xyphoid process

Osteology Superior view

Inferior view

Osteology

Anterior aspect

Posterior aspect

Osteology • Lateral border is thicker than medial – Because of all the muscle attachments

Osteology • Anteriorly – Glenoid Cavity • Shallow, ovalshaped depression – Coracoid Process • Looks like a bent finger

Osteology • Posteriorly – Separated by ribs by thin layers of muscle – Spine • Strong, sharp ridge

Osteology

Osteology

Osteology

Shoulder Girdle

Joints of the Shoulder • Sternoclavicular joint • Acromioclavicular joint • Coracoclavicular joint • Scapulothoracic joint • Glenohumeral joint

Sternoclavicular Joint • Strong enough so that dislocation of joint is less common than fracture of clavicle • Provides major axis of rotation for movement of clavicle and scapula • Elevation: 60°. • 24-30° motion anterior, posterior, and inferior • Helps position GH joint

Acromioclavicular Joint • Irregular diarthrodial joint between the acromion process of the scapula and the distal clavicle. – Allows limited motions in all three planes.

• Rotation occurs during arm elevation • Close-packed position with humerus abducted to 90 degrees

Coracoclavicular Joint • A syndesmosis with coracoid process of scapula – Bound to the inferior clavicle by the coracoclavicular ligament.

• Permits little movement

Scapulothoracic joint • Not a true joint • The movement of the scapula on the wall of the thoracic cage is critical to shoulder motion • Contraction of the scapular muscles that attach the scapula to the axial skeleton, is critical in stabilizing the scapula and providing a base for joint function

Glenohumeral Joint • Ball and socket joint in which the head of the humerus articulates with the glenoid fossa of the scapula • Referred to as the shoulder joint

Ligaments of the Sternoclavicular Joint • Interclavicular ligament – Strengthens the capsule superiorly

• Costoclavicular ligament – Limits elevation of the pectoral girdle

Ligament of the Acromioclavicular Joint • Acromioclavicular ligament – A fibrous band – This ligament strengthens the joint superiorly

Ligaments of the Coracoclavicular Joint • Coracoclavicular ligament – A strong pair of bands that unites the coracoid process of the scapula to the clavicle – Consists of two ligaments • Conoid ligament • Trapezoid

Ligaments of the Glenohumeral Joint • Glenohumeral ligaments - Strengthen the anterior aspect of the articular capsule

- Three fibrous bands Superior Glenohumeral ligament Taut during external rotation and plays a small role in the stability of the shoulder

Ligaments of the Glenohumeral Joint • Glenohumeral ligaments Middle Glenohumeral ligament Taut during external rotation and plays a small role in stability of the shoulder Inferior Glenohumeral Ligament Taut during external rotation, and plays a small role in stability of the shoulder

Ligaments of the Glenohumeral Joint • Coracohumeral ligament Strengthens the capsule superiorly Resists the pull of gravity and limits external rotation of the shoulder

• Transverse humeral ligament Strengthens the capsule and bridges the gap between the greater and lesser tubercles of the humerus keeps the biceps tendon in its groove during movements

Movements of the Shoulder Complex • Movements of the Scapula – Abduction (Protraction)

Movements of Scapula

Serratus Anterior

Movements of the Shoulder Complex • Movements of the Scapula – Adduction (Retraction)

Movements of Scapula

Trapezius

Rhomboid major and minor

Movements of the Shoulder Complex • Movements of the Scapula – Elevation

Movements of Scapula

Levator Scapulae

Trapezius Rhomboid major and minor

Movements of the Shoulder Complex • Movements of the Scapula – Depression

Movements of Scapula

Trapezius

Pectoralis minor

Serratus Anterior

Movements of the Shoulder Complex • Movements of the Scapula – Upward rotation

Movements of Scapula

Trapezius

Serratus Anterior

Movements of the Shoulder Complex • Movements of the Scapula – Downward rotation

Movements of Scapula

Levator Scapulae

Scapulohumeral Rhythm • A regular pattern of scapular rotation that accompanies and facilitates humeral abduction • Scapulothoracic : glenohumeral joint movements = 1:2

Composite Shoulder Girdle Movement

Composite Shoulder Girdle Movement

Composite Shoulder Girdle Movement

Composite Shoulder Girdle Movement

Shoulder Goniometry • Flexion / Extension – 1800 / 500-600

• Abduction/Adduction – 1800 / 450-500

• Internal/External Rotation – 700-800 / 800-900

• Horizontal Abduction / Horizontal Adduction – 450 / 1200

Movements of the Shoulder Complex

Movements of the Shoulder Complex • Movements of Glenohumeral joint – Flexion

Deltoid

Pectoralis major

Coracobrachialis

Biceps brachii

Movements of the Shoulder Complex • Movements of Glenohumeral joint – Extension

Teres major

Deltoid

Triceps brachii

Latissimus dorsi

Movements of the Shoulder Complex

Abduction

Adduction

Abduction • Movements of Glenohumeral joint – Abduction

Deltoid

Supraspinatus

Adduction • Movements of Glenohumeral joint – Adduction

Pectoralis major

Latissimus dorsi Teres major

Movements of the Shoulder Complex

External Rotation • Movements of Glenohumeral joint – Medial rotation

Infraspinatus

Teres minor

Internal Rotation • Movements of Glenohumeral joint – Medial rotation

Internal Rotation The body limits internal rotation thus placing the arm behind the body increases the amount of internal rotation

Subscapularis Latissimus dorsi

Pectoralis major

Teres major

Movements of the Shoulder Complex

Biomechanics of GH Stability • The normal shoulder constrains the humeral head to the center of the glenoid cavity throughout most of the arc of movement – Static restraints – Dynamic restraints

Static restraints • • • •

Glenoid labrum and articular surfaces Negative intra-articular pressure Ligaments and capsule Joint fluid adhesiveness

Dynamic restraints • Rotator cuff muscles • Deltoid and biceps • Concavity compression

Rotator Cuff

Rotator Cuff

Stability Ratio • Maximal displacing force in a given direction(perpendicular to glenoid center line) that can be stabilized by compressive load • Affected by – Glenoid/labrum depth – rim lesions – Glenoid version – Dynamic stabilizer compromise

Load on the Shoulder

Load on the Shoulder